Heavily armed officers remained on guard at the Marikana platinum mine to the north-west of Johannesburg on Friday, after killing more than two dozen striking miners on Thursday night.

Police Minister Nathi Mthethwa told Talk Radio 702 that at least 30 people had died in the operation at the mine, saying a group of 3,000 people had not dispersed when ordered to.

"A lot of people were injured and the number keeps going up," Mthethwa told the radio station, also defending his officers. "From amongst the crowd, people opened fire on police and the police retaliated."

The police minister said he had requested that South African President Jacob Zuma order an investigation into the incident.

The secretary general of the National Union of Mineworkers (NUM), Frans Baleni, said in an interview on local radio that 36 people had died.

The miners were said to be armed with machetes, sticks and other rudimentary weapons.

"Police did everything they could …but people - the miners - said they were not leaving and are prepared to fight," Mthethwa said.

Half an ounce per annum

Unrest flared at the platinum mine earlier in the week, initially as a confrontation between two rival mining unions. The Association of Mineworkers and Construction Union (AMCU) is a rival body seeking to challenge the long-dominant NUM, which is closely allied to the ruling ANC party in South Africa.

The striking workers were also calling for pay rises in the initial protests, saying their pay should be more than doubled. According to a local business report on the iol.co.za website, the rock drill operators are currently paid 5,000 South African rand (489 euros, $605) per annum and were seeking 12,500 rand instead. An ounce of platinum currently costs over $1,400.

The Marikana mine is the flagship platinum site for British company Lonmin, with South Africa producing roughly 80 percent of the world's platinum. Platinum prices, having slumped by over a quarter in the past year, spiked by over 10 percent on Friday morning. Lonmin shares, meanwhile, turned south amid the violence. The company's shares were already seriously slumping before the unrest, having shed more than half of their previous value since the end of 2010.

Police, armored vehicles and helicopters were stationed at the mine on Friday morning, seeking to ensure calm following the overnight deaths.

msh/rc (AFP, dpa, Reuters)